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Employee Benefit and Deferred Compensation Plans - Additional Information (Details) | 12 Months Ended
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Dec. 31, 2018 USD ($) point plan shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2007 officer
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Accumulated benefit obligation | $ 24,945,000 | $ 27,859,000 |  |
Retiring age limit, minimum | 55 years |  |  |
Retiring age limit, maximum | 65 years |  |  |
Eligible employee from service (in years) | 15 years |  |  |
Number of points for eligibility (points) | point | 70 |  |  |
Minimum eligible age for Medicare coverage | 65 years |  |  |
Life insurance coverage face value | $ 5,000 |  |  |
Life insurance maturity age | 70 years |  |  |
Additional life insurance maturity age | 70 years |  |  |
Expected company contributions | $ 156,000 |  |  |
Health care cost trend rate (percent) | 5.60% |  |  |
Percentage of plan compensation as nondiscretionary contribution (percent) | 5.00% |  |  |
Percentage of plan compensation in excess of social security wage base (percent) | 5.00% |  |  |
Hours of service credited to the employees during the year | 1000 hours |  |  |
Redemption notice | 60 days |  |  |
Employee deferrals (percent) | 4.00% |  |  |
Employee deferrals amounts | $ 13,477,000 | 11,471,000 | $ 10,762,000 |
Number of officers provided for | officer |  |  |  | 4
Expiration period subsequent to retirement |  |  |  | 15 years
Supplemental executive retirement liabilities totaled | $ 3,865,000 | 3,846,000 |  |
Number of conventional deferred compensation plans | plan | 2 |  |  |
Company's deferred compensation plan expense | $ 1,290,000 | 1,935,000 | 1,537,000 |
Incentive compensation plan expense | $ 5,117,000 | $ 4,490,000 | $ 2,307,000 |
Option expiration period | 10 years |  |  |
Granted (shares) | shares | 0 | 0 | 0 |
Intrinsic value of options exercised | $ 1,180,000 | $ 2,487,000 | $ 8,323,000 |
Fair value of options vested in period |  |  | 78,000 |
Common shares reserved for issuance under employee benefit plans (shares) | shares | 2,043,402 |  |  |
Stock compensation plan |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Compensation expense | $ 0 | 0 | 0 |
Unrecognized stock-based compensation expense | 0 |  |  |
Performance- Based Restricted Stock |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Compensation expense | 7,251,000 | 5,293,000 | 3,117,000 |
Time- Based Restricted Stock |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Unrecognized stock-based compensation expense | $ 7,909,000 |  |  |
Weighted average period over which unrecognized expense is expected to be recognized (in years) | 1 year 5 months 13 days |  |  |
Growth Investment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 55.00% |  |  |
Real Estate | Growth Investment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 5.00% |  |  |
Interest Rate Contract | Growth Investment |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 45.00% |  |  |
Minimum | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 65.00% |  |  |
Minimum | Debt Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 25.00% |  |  |
Maximum | Equity Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 75.00% |  |  |
Maximum | Debt Securities |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Equity income strategy (percent) | 35.00% |  |  |
Pension Benefits |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Company contribution to pension benefit plan | $ 0 | 0 |  |
Accumulated benefit obligation | 24,945,000 | 27,859,000 | $ 28,012,000 |
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Company contribution to pension benefit plan | $ 89,000 | $ 119,000 |  |

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